dbchecker: Fixing up incorrect DNs wasn't working

dbchecker: Fixing up incorrect DNs wasn't working

dbcheck would fail to fix up attributes where the extended DN's GUID is
correct, but the DN itself is incorrect. The code failed attempting to
remove the old/incorrect DN, e.g.

 NOTE: old (due to rename or delete) DN string component for
 objectCategory in object CN=alice,CN=Users,DC=samba,DC=example,DC=com -
 <GUID=7bfdf9d8-62f9-420c-8a71-e3d3e931c91e>;
   CN=Person,CN=Schema,CN=Configuration,DC=samba,DC=bad,DC=com
 Change DN to <GUID=7bfdf9d8-62f9-420c-8a71-e3d3e931c91e>;
   CN=Person,CN=Schema,CN=Configuration,DC=samba,DC=example,DC=com?
 [y/N/all/none] y
 Failed to fix old DN string on attribute objectCategory : (16,
 "attribute 'objectCategory': no matching attribute value while deleting
 attribute on 'CN=alice,CN=Users,DC=samba,DC=example,DC=com'")

The problem was the LDB message specified the value to delete with its
full DN, including the GUID. The LDB code then helpfully corrected this
value on the way through, so that the DN got updated to reflect the
correct DN (i.e. 'DC=example,DC=com') of the object matching that GUID,
rather than the incorrect DN (i.e. 'DC=bad,DC=com') that we were trying
to remove. Because the requested value and the existing DB value didn't
match, the operation failed.

We can avoid this problem by passing down just the DN (not the extended
DN) of the value we want to delete. Without the GUID portion of the DN,
the LDB code will no longer try to correct it on the way through, and
the dbcheck operation will succeed.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13495

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Pair-programmed-with: Andrew Bartlett <abartlet@samba.org>